The present invention is directed to curing by radiation, particularly electron-beam (EB) radiation, of pressure-sensitive, acrylic-based interpolymers containing an interpolymerized amount of tackifier monomers, as defined herein.
U.S. Pat. No. 2,544,692 to Kuegler et al discloses copolymerization of an acrylic acid with minor amounts of a fumarate diester. Emulsion and bulk polymerization are stated as being feasible. A pressure-sensitive-adhesive product is disclosed.
U.S. Pat. No. 2,642,414 to Bauer et al discloses copolymers of esters of methacrylic acid, a saturated aliphatic monohydric alcohol, a maleinoid ester of a saturated aliphatic monohydric alcohol of from 4 to 14 carbon atoms, and certain organic acids. The maleinoid esters include dibutyl fumarate. The products of the reaction are disclosed to have utility in modifying the pour point of hydrocarbon oils.
U.S. Pat. No. 4,220,744 to Tulacs et al discloses the use of two-stage bulk polymerization to form a viscous liquid containing interpolymerized amounts of dialkyl esters of fumaric or maleic acid.
The curing of monomers as well as polymers to induce or improve pressure-sensitive properties is old in the art. Of relevance to the overall concept is U.S. Pat. No. 3,725,115 to Christenson et al, who disclose the preparation of pressure-sensitive adhesives by irradiating a hot-melt composition. The compositions disclosed are coated on release liners and subjected to electron-beam radiation of a dosage of from 6 to 8 megarad (60 to 80 kiloGray), leading to high peel strengths. The improved adhesive is then transferred to the face stock.
U.S. Pat. No. 4,069,123 to Skoultchi et al discloses the UV curing of homopolymers of alkyl esters of acrylic and methacrylic acids and of copolymers of such monomers with other comonomers, including C.sub.1 -C.sub.4 alkyl half-esters of maleic and fumaric acids. The polymers are disclosed as being formed by bulk, solvent or emulsion polymerization.
It has not been heretofore known to use C.sub.1 -C.sub.3 lower alkyl diesters of unsaturated dicarboxylic acids in combination with energy curing, to enhance adhesive properties. This, in part, is the subject matter of the instant invention.